A double-blind placebo controlled comparison of methylphenidate and dextroamphetamine treatments of 48 hyperactive boys has both adverse effects and clinical response to the two drugs. Clinical response rate measured by classroom behavior, home behavior, cognitive test performance and overall global improvement is extremely high - 96% - when both drugs are tried over a wide dose range. "Non-responders" are most often children who suffer adverse effects and these typically differ across the two stimulants. Methylphenidate is more likely to cause tics in combination with over focused ideation, a more "Tourette Disorder" form of behavior; dextroamphetamine is more likely to cause obsessive compulsive ideation and rituals that resemble clinical obsessions and compulsions, with cleaning and neatening behaviors most prominent. These different patterns of adverse response may relate to subtle differences in the effect of the two stimulants on central metabolism of serotonin and dopamine.